Volumetric dry solids materials feeders are designed to discharge material such as powders, granules, or stranded fiberglass at a predetermined rate based on volume. The material typically flows out of a hopper into a trough. Located in the trough is a discharge device, such as an auger, which feeds the material out of the trough through a discharge opening or spout. Such feeders, especially when feeding adhesive, cohesive, fibrous, or hygroscopic dry solids materials, sometimes experience problems in transferring the material from the hopper to the discharge device due to the material either sticking to the walls of the hopper, blocking downward flow, or bridging (compaction) of the material in the trough and/or hopper. Problems are also sometimes experienced in properly filling the feed auger with material.
It has been found that the above problems, among others, are reduced by the application of high-frequency vibration to the trough and hopper, particularly during handling of certain types of short fiberglass strands and other kinds of fibrous products. The high-frequency vibration shakes the material loose from the walls of the hopper, breaks-up bridging material, and greatly assists in filling the feed auger.
In addition to material-flow problems within the hopper or trough, the precise metering of material by a volumetric feeder can be disrupted, for example, when material of varying density enters the auger, when material sticks to the auger, or when difficulty is experienced in properly filling the auger. It has been found that vibration of the trough and auger also minimizes these problems. It is therefore desirable in many metering applications to vibrate both the hopper and the trough/auger.
Prior attempts at solving feeding problems through vibration include Wahl, U.S. Pat. No. 3,151,782, which discloses a volumetric materials feeder in which a single motor powers a metering auger and a vibratory mechanism. A first shaft of the vibratory mechanism imparts vibration to the trough and auger by rotation of an eccentric weight, and a second shaft, perpendicular to and directly connected by a belt/pulley system to the first shaft, vibrates the hopper. The frequency of hopper and trough vibrations will thus be equal, which, combined with the direct connection of the two vibration shafts, can sometimes cause problems of vibration interference (primarily harmonic problems).
Wahl, U.S. Pat. No. 3,297,203, discloses a vibratory tray volumetric feeder having a vibratory mechanism that vibrates both the tray and also an auxiliary hopper below the supply hopper. As in the Wahl '782 patent described above, the hopper and tray are both directly connected to the vibratory mechanism, with that configuration's attendant interference problems.
Wahl, U.S. Pat. No. 3,411,675, discloses a double auger volumetric feeder in which the trough and hopper are vibrated by means of a rotating cam repeatedly striking a protrusion connected to the support platform of the hopper and trough. Such a vibratory mechanism is subject to undue wear, along with the interference problems described above.